Ms. Mann, of course, is known for taking startlingly revealing photographs of her own young children, pictures that have raised concern about the effects of such exposure on children. But Mr. Cantor says Ms. Mann's photos, many of which showed her children nude, were far more invasive than his show. "Sally threw this childhood innocence thing to the wolves," he said.
Yet perhaps because he became a parent himself for the first time last year, Mr. Cantor says he has been protective of Frankie. "If he cries too easily, I don't want people to think he's a sissy. If he hadn't learned to ride his bike after he cried, we wouldn't have used it. If that makes it less real, so be it."

'So' is typically classified as an adverb, although it has clear pronominal affinities when used, as here, as a preposed copular complement. The subject is 'it', and 'be' here is not an infinitive but the imperative mood (sometimes termed an 'optative subjunctive').

'So be it' (=let it be so) is a set expression indicating the speaker's resignation to, or acceptance of, a certain state of affairs.